# Chemical Formula for Barium Chloride

Barium Chloride is represented as $\ce{BaCl2}$.

Since chlorine is a diatomic molecule, It should be denoted as $\ce{Cl2}$.

Formulating, we get

\begin{array}{|c:cc|}\hline \small \rm Element & \ce{Ba} & \ce{Cl2}\\ \small \rm Valency & 2 & 1 \\\hline \end{array}

Crisscrossing the valencies of Barium and Chlorine we get $\ce{Ba(Cl2)2}$ — as opposed to the accepted formula of $\ce{BaCl2}$. How is it so?

• In barium chloride, the chlorine is not in the form of a diatomic molecule. Think about how ionic compounds are formed. – M.A.R. Jun 19 '16 at 6:17
• @TIPS How are they formed in this case? – Good Guy Jun 19 '16 at 6:27
• Valency is a property of an element, not a molecule. – Ivan Neretin Jun 19 '16 at 7:55
• @IvanNeretin How do you obtain the formula for Barium Chloride then? – Good Guy Jun 19 '16 at 9:12
• Much like you did, except don't mention $\ce{Cl2}$ at all. There is just Cl, its valency is 1, and then there is Ba with valency 2, so... – Ivan Neretin Jun 19 '16 at 13:52

When they react, a barium atom will give up two electrons to form a action, and a chlorine molecule will pick up two electrons to form a pair of chloride ions: $$\ce{Ba -> Ba^2+ +2e^-}$$ $$\ce{Cl2 +2e^- -> 2Cl^-}$$ When you have both of those things at once, the electrons are "consumed" as fast as they are "produced", so they don't appear at all in the result: $$\ce{Ba +Cl2->Ba^2+ +2Cl^-}$$ which forms an ionic lattice when solid. Since this lattice has overall neutral charge, its ionic charges must balance with integer coefficients.
Funnily enough, these coefficients are $1$ and $2$ for $2+$ and $1-$ respectively, so these are applied to the ions which carry those charges. Thus: $$\ce{Ba1Cl2}$$ or more simply and directly: $$\ce{BaCl2}$$
When chlorine is in its free state it is diatomic. But when it reacts with barium it is not in the form of $\ce{Cl2}$. It will be in its ionic state which is $\ce{Cl-}$. The same goes for Barium. Barium is mono-atomic and its ionic state is $\ce{Ba^2+}$. Barium gives one electron to a chlorine atom and another electron to another chlorine atom, as valency of chlorine is 1, so it is $\ce{BaCl2}$.